The present invention relates to disposable absorbent articles. More particularly, the invention relates to an economical method for advantageously modifying the physical properties of a nonwoven fibrous web for use as a component of a disposable absorbent article, and to disposable articles incorporating such modified nonwoven webs.
Disposable, wearable articles having an inner, body-facing, absorbent, liquid-retaining component and an outer, garment-facing, liquid-impervious component are well known. Articles of that type are commonly available in the form of disposable diapers, disposable underwear, pull-on diapers and training pants, incontinence pads, incontinence briefs, sanitary napkins, and the like. Such articles generally include a flexible, liquid-impervious backsheet that is adapted to be positioned between an absorbent component of the article and the clothing of the wearer, to prevent wetting or soiling of the wearer""s clothing when the article is in use.
In addition to imperviousness to liquids, the backsheet also preferably includes a cloth-like outer surface, which provides a softer feel, and also a more appealing visual appearance, as compared with the outer surface of a smooth, flat plastic film. Two-ply backsheets that provide a desirable, more cloth-like appearance for such disposable, wearable articles are also known. In that regard, U.S. Pat. No. 5,151,092, entitled xe2x80x9cAbsorbent Article with Dynamic Elastic Waist Feature Having a Predisposed Resilient Flexural Hinge,xe2x80x9d which issued on Sep. 29, 1992, to Kenneth B. Buell, et al., discloses a disposable diaper backsheet formed either from a woven or a nonwoven material, a polymeric film, or a composite material in the form of a film-coated, nonwoven material. That patent also discloses the step of embossing of a plastic film backsheet to provide a more cloth-like visual appearance to a plastic film.
Also known to those skilled in the art are methods for imparting stretchability to an otherwise substantially inelastic material, which may be employed as a backsheet. For example, the use of corrugating rolls to laterally or longitudinally stretch and to simultaneously provide a corrugated form to thin plastic films is disclosed in U.S. Pat. No. 4,116,892, entitled xe2x80x9cProcess for Stretching Incremental Portions of an Orientable Thermoplastic Substrate and Product Thereof,xe2x80x9d which issued on Sep. 26, 1978, to Eckhard C. A. Schwarz; U.S. Pat. No. 4,834,741, entitled xe2x80x9cDiaper With Waistband Elastic,xe2x80x9d which issued on May 30, 1989, to Reinhardt N. Sabee; U.S. Pat. No. 5,156,793, entitled xe2x80x9cMethod for Incrementally Stretching Zero Strain Stretch Laminate Sheet In A Non-Uniform manner To Impart A Varying Degree Of Elasticity Thereto,xe2x80x9d which issued on Oct. 20, 1992, to Kenneth B. Buell et al.; U.S. Pat. No. 5,167,897, entitled xe2x80x9cMethod for Incrementally Stretching A Zero Strain Stretch Laminate Sheet To Impart Elasticity Thereto,xe2x80x9d which issued on Dec. 1, 1992 to Gerald M. Sheeter et al.; and U.S. Pat. No. 5,422,172, entitled xe2x80x9cElastic Laminated Sheet of An Incrementally Stretched Nonwoven Fibrous Sheet and Elastomeric Film and Method,xe2x80x9d which issued on Jun. 6, 1995, to Pai-Chuan Wu. The corrugating rolls disclosed in each of those patents are employed in carrying out a process sometimes referred to as xe2x80x9cring-rolling,xe2x80x9d to locally stretch and form corrugations in the material, in order to impart a greater degree of stretchability to selected portions of a sheet or web that may serve as a backsheet for disposable absorbent articles. Such backsheets can include both a polymeric film and an overlying and contacting layer of nonwoven, fibrous material.
In addition to incorporation into backsheets, nonwoven materials can also be incorporated into and form a part of a liquid-pervious topsheet, as well as in leg cuffs that are provided to minimize leakage from the article. Other structural members of disposable absorbent articles can also include nonwoven elements, particularly where stretchability of the material is a desirable attribute for providing improved fit of the article.
In order to provide improved comfort to the wearer of disposable absorbent articles, certain components of the articles, such as a backsheet, in addition to providing imperviousness to liquids, desirably permit the passage therethrough of moisture vapor and also preferably air, to help maintain dryness and to reduce the humidity adjacent the wearer""s body. An impervious polymeric film to which breathability has been imparted to allow air and moisture vapor transmission through the film is disclosed U.S. Pat. No. 3,156,342, entitled xe2x80x9cFlexible Absorbent Sheet,xe2x80x9d which issued on Nov. 10, 1964, to G. A. Crowe, Jr.; U.S. Pat. No. 3,881,489, entitled xe2x80x9cBreathable, Liquid Impervious Backsheet for Absorbent Devices,xe2x80x9d which issued on May 6, 1975 to Edward Wallace Hartwell, et al.; U.S. Pat. No. 3,989,867, entitled xe2x80x9cAbsorbent Devices Having Porous Backsheet,xe2x80x9d which issued on Nov. 2, 1976, to James Bryant Sisson; U.S. Pat. No. 4,153,751, entitled xe2x80x9cProcess for Stretching an Impregnated Film of Material and The Microporous Product Produced Thereby,xe2x80x9d which issued on May 8, 1979, to Eckhard C. A. Schwarz; and U.S. Pat. No. 4,539,256, entitled xe2x80x9cMicroporous Sheet Material, Method of Making and Articles Made Therewith,xe2x80x9d which issued on Sep. 3, 1985, to Gene H. Shipman.
Although there have been significant product improvements in recent years that have resulted in improved functioning and increased consumer acceptance of disposable absorbent articles, it is still desirable to provide an economical way to form for use in such articles a stretchable nonwoven material having optimal physical properties, which may for example be employed in a backsheet that is impervious to liquids, that is pervious to moisture vapor and also preferably air, and that additionally has a soft, cloth-like outer surface.
Accordingly, it is an object of the present invention to provide an economical method for advantageously modifying a pre-formed, nonwoven fibrous web to have desirable properties which can be used as a component or an extensible component of a disposable absorbent article.
It is another object of the present invention to provide a method for making a relatively inexpensive, flexible composite material which can be used in a disposable absorbent article, wherein the composite material may include the attribute of liquid-imperviousness, and the desirable attribute of perviousness to moisture vapor and also preferably air, as well as the desirable attribute of a soft, cloth-like feel on at least one of its surfaces.
It is a further object of the present invention to provide a method for economically modifying a pre-formed, nonwoven fibrous web and joining it to an elastic component to create a composite material which can be advatageously used as a elastically stretchable, and if desired breathable, component of a disposable absorbent article.
Briefly stated, in accordance with one aspect of the present invention, an economical method is provided for advantageously modifying the physical characteristics of a pre-formed, nonwoven fibrous web. The method includes feeding in a web movement direction to a pair of opposed forming rolls a substantially untensioned, nonwoven fibrous web having an initial width, thickness, basis weight, low-elongation cross-web extensibility expressed as an initial load to achieve 10% cross-web elongation, intermediate-elongation cross-web extensibility expressed as an initial load to achieve 30% cross-web elongation, cross-web strength, and elongation capability. The web is gripped between the forming rolls at a nip defined by the forming rolls. Each forming roll includes a plurality of axially spaced, circumferentially extending, alternating radial teeth and intervening grooves that are in interengaged condition, with the teeth of each roll extending into the grooves of the opposed roll.
The gripped nonwoven web is subjected to incremental lateral stretching by passing the web between the interengaged forming rolls while the rolls are rotating in opposite directions to incrementally stretch the web in a lateral, cross-web (i.e., xe2x80x9ccross-machinexe2x80x9d or CD) direction that is substantially perpendicular to the longitudinal, web movement (i.e., xe2x80x9cmachinexe2x80x9d or MD) direction. The incrementally stretched web is then withdrawn from between the forming rolls by applying to the stretched web a substantially uniform tensile force in the web movement direction as the web passes from the forming rolls, to stretch the web in the web movement direction to obtain a modified web which has a load to achieve 10% cross-web elongation of from about 5% to about 100% of the initial load to achieve 10% cross-web elongation, a load to achieve 30% cross-web elongation of from about 5% to about 100% of the initial load to achieve 30% cross-web elngation, a cross-web strength of from about 10% to about 80% of the initial cross-web strength, and an elongation capability of from about 105% to about 200% of the initial cross-web elongation capability. The web may also have a modified web width that is from about 25% to about 300% of the initial web width, a modified web thickness that is from about 85% to about 400% of the initial web thickness, and a modified basis weight that is less than, equal to, or greater than the initial web basis weight.
In accordance with another aspect of the present invention, a method is provided for combining a modified nonwoven fibrous web of the invention with a polymeric film, or with an elastic member, which may be liquid-impervious, yet breathable.
In accordance with still another aspect of the present invention, a method is provided for making a liquid-impervious, breathable material which can be used, for example, as a backsheet for a disposable absorbent article having a soft, cloth-like, outermost surface. The method includes providing a nonwoven fibrous web having its physical properties modified by having passed through a pair of forming rolls. A thermoplastic polymeric film is provided that includes an incompatible inorganic material dispersed therewithin to provide a plurality of discrete, spaced regions of inorganic material within a polymer matrix. The polymeric film includes a first face and a second face. The modified fibrous nonwoven web is then combined with the polymeric film to form a composite web, wherein the second face of the polymeric film defines an outwardly-facing surface of the composite web. The composite web is then passed between a pair of opposed, closely spaced forming rolls each having a plurality of alternating teeth and grooves that are in intermeshing relationship. The forming rolls impart cross-web tensile forces to the composite web, which provides micropores within the polymeric film as a result of localized stretching of the film to cause localized separation of the thermoplastic polymer from the incompatible material to provide the micropores. The micropores so provided are of a size that permits the passage through the composite web of air and moisture vapor but substantially prevents the passage therethrough of liquids.
The present invention also includes the soft, cloth-like, liquid-impervious and breathable backsheets, and other absorbent article components, such as topsheets, cuffs and other structural members that are formed by incorporating a nonwoven fibrous web that has been modified in accordance with the methods herein described.